Abstract: Since 1966, the U.S.-U.K. cross-national project has studied differences between the United States and United Kingdom in psychiatric diagnostic practice, in the frequency and type of psychiatric, medical and social disorders, and in patterns of health care. An important part of this work has been the development of reliable and valid methods for describing subjects in the two countries. During 1971 and 1972 the project focused on hospitalized geriatric patients, and since 1973 has extended its geriatric work into a community survey of aged persons, comparing the prevalence of psychiatric, medical and social disorders between New York and London. Extensive data (some 1500 items of information) have been collected on over 400 randomly selected elderly residents of New York and a comparable number of randomly selected elderly residents of London. A one-year follow-up study is just about complete. It is the purpose of this research project to use the data already collected to derive reliable and valid summary indicators of psychiatric, medical and social functioning in the elderly, and in turn to use these indicators to generate valid typologies for classifying the elderly according to these areas of functioning.